Electro-hydraulic steering system for an articulated vehicle

ABSTRACT

The present invention provides an electro-hydraulic steering system for an articulated vehicle having a front frame and a rear frame. The system includes a controller and a hydraulic steering system having a pump for providing hydraulic pressure. A steering input control, typically a steering wheel, transmits mechanical steering inputs to the hydraulic steering system. A pair of articulation cylinders rotate the front frame with respect to the rear frame in response to hydraulic pressure to steer the vehicle. Position sensors transmit input signals to the controller indicating the position of the steering input control and each of the articulation cylinders. An electro-hydraulic valve receives electrical control signals from the controller to control the hydraulic pressure to each articulation cylinder. In this manner, the present invention can perform steering performance enhancements, such as snubbing, steering jerk limit control, and electronic steering adjustment.

TECHNICAL FIELD

The present invention relates generally to an electro-hydraulic steeringsystem for an articulated vehicle.

BACKGROUND ART

An articulated vehicle is a vehicle having a front frame member, a rearframe member, and an articulation joint connecting the front and rearframe members. Typically, to steer an articulated vehicle right or left,the front frame member must be rotated relative to the longitudinal axisof the rear frame member about the articulation joint.

To rotate the front frame member, these vehicles commonly includearticulation cylinders mounted to the rear frame member. Thearticulation cylinders are operated in opposite directions. That is,when one cylinder is extended forward, the other cylinder is retractedrearward and vice versa. Typically, the articulation cylinders arehydraulically controlled by a steering system commonly known as a handmetering steering unit or HMU.

Although prior art HMUs provide adequate steering control, they haveseveral shortcomings. Foremost, hand metering steering units can notperform certain steering performance enhancements, such as snubbing,steering jerk limit control, and electronic steering adjustment.Snubbing is defined as the softening of the end of cylinder impact.Thus, it is desirable to provide an electro-hydraulic steering systemfor an articulated vehicle which overcomes the shortcomings of the priorart.

DISCLOSURE OF THE INVENTION

The present invention provides an electro-hydraulic steering system foran articulated vehicle having a front frame and a rear frame. The systemincludes a controller and a hydraulic steering system having a pump forproviding hydraulic pressure. A steering input control, typically asteering wheel, transmits mechanical steering inputs to the hydraulicsteering system. A pair of articulation cylinders rotate the front framewith respect to the rear frame in response to hydraulic pressure tosteer the vehicle. Position sensors transmit input signals to thecontroller indicating the position of the steering input control andeach of the articulation cylinders. An electro-hydraulic valve receiveselectrical control signals from the controller to control the hydraulicpressure to each articulation cylinder. In this manner, the presentinvention can perform steering performance enhancements, such assnubbing, steering jerk limit control, and electronic steeringadjustment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic top view of a wheel loader; and

FIG. 2 is a schematic block diagram of an electro-hydraulic steeringsystem for the wheel loader.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to the Figures, wherein like numerals indicate like orcorresponding parts throughout the several views, a schematic top viewof a wheel loader 10 is shown in FIG. 1. The wheel loader 10, alsoreferred to as a front loader, is used primarily to scoop, lift, andmove large quantities of material, such as earth. Although a wheelloader is illustrated in FIG. 1, one of ordinary skill in the art willrecognize that the present invention may be used on any vehicle havingan articulated steering system, such as for example, a scraper motorgrader etc. In other words, the present invention may be used on anyvehicle which must be articulated to turn. Accordingly, the wheel loader10 is illustrated in FIG. 1 for example purposes only and is notintended to limit the scope of the present invention.

The wheel loader 10 includes a front frame 12, a rear frame 14, and abucket 16. The front and rear frames 12 and 14 are supported by tires18. An operator cab, shown generally at 20, contains the many controlsnecessary to operate the wheel loader 10. The operator cab 20 istypically mounted on the rear frame 14. An engine, shown generally at22, is used to drive or power the wheel loader 10. The engine 22 ismounted on the rear frame 14. The bucket 16 is used to scoop and liftmaterial. The bucket 16 is mounted to the front frame 12 with a pair oflift arms 24 and 26. The lift arms 24 and 26 are hydraulicallycontrolled to lift and tilt the bucket 16.

As will be readily understood by one of ordinary skill in the art aright articulation cylinder, located generally at 28, is mounted to theright side of the rear frame 14 and a left articulation cylinder,located generally at 30, is mounted to the left side of the rear frame14. The right and left articulation cylinders 28 and 30 are used torotate the front frame 12 about an articulation joint 32. Thearticulation joint 32 connects the front frame 12 and the rear frame 14.To rotate the front frame 12 to the right, the right articulationcylinder 28 is retracted rearward and the left articulation cylinder 30is extended forward. To rotate the front frame 12 to the left, the rightarticulation cylinder 28 is extended forward and the left articulationcylinder 30 is retracted rearward. Each articulation cylinder 28 and 30has a range of movement between an extended end position and a retractedend position.

In FIG. 1, the front frame 12 of the wheel loader 10 is shown rotated toa full left articulation angle +θ. The articulation angle θ is formed bythe intersection of the longitudinal axis A of the front frame 12 andthe longitudinal axis B of the rear frame 14. Each articulation cylinder28 and 30 includes a position sensor for indicating the extended orretracted position of the cylinder. With this information, thearticulation angle θ may be calculated. Alternatively, a rotary sensormay be positioned at the articulation joint 32 to measure thearticulation angle θ. A full right articulation angle -θ, shown inphantom lines in FIG. 1, is a mirror image of the full left articulationangle +θ. The wheel loader 10 may be operated with the front frame 12rotated to the full left articulation angle +θ, the full rightarticulation angle -θ, or any angle therebetween. To steer the wheelloader 10 left, the front frame 12 is rotated to a left articulationangle. To steer the wheel loader 10 right, the front frame 12 is rotatedto a right articulation angle.

FIG. 2 is a schematic block diagram of an electro-hydraulic steeringsystem 40 for the wheel loader 10. The steering system 40 is designed tocontrol the articulation angle θ of the wheel loader 10. The system 40includes a steering input control, represented by block 42, whichtransform the actions of an operator's hands into mechanical movementsand electrical input signals. Typically, the steering input control 42is a steering wheel. The mechanical movements are input into mechanicaland hydraulic steering controls, represented by block 44. The electricalinput signals carry steering information to an electronic controlcomputer, represented by block 46.

The mechanical and hydraulic steering controls 44 are adjusted by themechanical movements of the steering input control 42 and combine with ahydraulic pump, described below, to produce high hydraulic pressure.

The control computer 46 receives the electrical input signals producedby the steering input control 42, processes the steering informationcarried by the input signals, and transmits electrical control signalsto an electro-hydraulic unit assembly, represented by block 48. Theelectro-hydraulic unit assembly 48 includes an electro-hydraulicdirectional valve, represented by block 54, and a main hydraulic valve,represented by block 56. As will be appreciated by one of ordinary skillin the art, the electro-hydraulic directional value and main hydraulicvalue are standard readily available values.

The hydraulic portion of the steering system 40 requires both highhydraulic pressure and low pilot pressure. High hydraulic pressure isprovided by a hydraulic pump, represented by block 50. The hydraulicpump 50 receives a rotary motion, typically from the engine 22 of thewheel loader 10, and produces high hydraulic pressure. Low pilotpressure is provided by a hydraulic pressure reducing valve, representedby block 52. The hydraulic pressure reducing valve 52 receives highhydraulic pressure from the hydraulic pump 50 and supplies low pilotpressure to the directional valve 54. The reducing value is a standardreadily available value.

The directional valve 54 includes an electrical solenoid and a hydraulicvalve. The solenoid receives electrical control signals from theelectronic control computer 46 and produces a controlled mechanicalmovement of a core stem of the valve 54. The hydraulic valve receivesboth the controlled mechanical movement of the core stem of the valve 54and low pilot pressure from the hydraulic pressure reducing valve 52 andproduces controlled pilot hydraulic pressure for the main hydraulicvalve 56.

The main hydraulic valve 56 receives both controlled pilot hydraulicpressure from the electro-hydraulic directional valve 54 and highhydraulic pressure from the hydraulic pump 50 and the mechanical andhydraulic steering controls 44, and produces controlled high hydraulicpressure for the articulation cylinders 28 and 30.

The articulation cylinders 28 and 30 receive controlled high hydraulicpressure from the main hydraulic valve 56 and produce a mechanicalmovement to rotate the front frame 12 of the loader 10. As describedabove, rotation of the front frame 12 of the loader 10 with respect tothe rear frame 14 of the loader 10 establishes the articulation angle θ.

The steering input control 42 and the articulation cylinders 28 and 30include electronic position sensors, represented by block 58. Theelectronic position sensors 58 transmit information regarding theposition of the steering input control 42 and each articulation cylinder28 and 30 to the control computer 46. With this position information,the control computer 46 can perform steering performance enhancements,such as snubbing, steering jerk limit control, and electronic steeringadjustment.

In order to create snubbing, the control computer 46 can detect when thearticulation cylinders 28 and 30 are approaching an end position andtransmit electrical control signals to the electro-hydraulic valve 54 toprevent a slam, or an abrupt halt in the movement of the articulationcylinders 28 and 30, as the end position is reached. To limit steeringjerk, the control computer 46 can detect an abrupt change in theposition of the steering input control 42 and transmit electricalcontrol signals to the electro-hydraulic valve 54 to prevent an abruptchange in the hydraulic pressure delivered to each articulation cylinder28 and 30 or, in other words, to prevent an abrupt movement of thearticulation cylinders 28 and 30. To perform electronic steeringadjustment, the control computer 46 can monitor the position of thesteering input control 42 and transmit electrical control signals to theelectro-hydraulic valve 54 to ensure that the articulation angle θ, ascalculated from the position of each articulation cylinder 28 and 30,corresponds with the position of the steering input control 42.

In the event of an electrical power failure, the mechanical andhydraulic steering controls 44 would directly operate the main hydraulicvalve 56 to provide limited emergency steering power.

Industrial Applicability

The present invention relates generally to an electro-hydraulic steeringsystem 40 for an articulated vehicle 10 having a front frame 12 and arear frame 14. A steering input control 42, typically a steering wheel,transmits mechanical steering inputs to the hydraulic steering system40. A pair of articulation cylinders 28, 30 rotate the front frame 12with respect to the rear frame 14 in response to hydraulic pressure 48to steer the vehicle. Position sensors 58 transmit input signals to thecontroller 46 indicating the position of the steering input control 42and each of the articulation cylinders 28, 30. An electro-hydraulicvalve 48 receives electrical control signals from the controller 46 tocontrol the hydraulic pressure to each articulation cylinder 28, 30. Inthis manner, the present invention can perform steering performanceenhancements, such as snubbing and steering jerk limit control, andelectronic steering adjustment.

The invention has been described in an illustrative manner, and it is tobe understood that the terminology which has been used is intended to bein the nature of words of description rather than of limitation.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims, whereinreference numerals are merely for convenience and are not to be in anyway limiting, the invention may be practiced otherwise than asspecifically described.

I claim:
 1. An electro-hydraulic steering system for an articulatedvehicle having a front frame and a rear frame, the system comprising:acontroller; a hydraulic steering system including a pump for providinghydraulic pressure; a steering input control for transmitting mechanicalsteering inputs to said steering system; at least one articulationcylinder for rotating the front frame with respect to the rear frame inresponse to hydraulic pressure to steer the vehicle; position sensorsfor transmitting input signals to said controller indicating theposition of said steering input control and each of said articulationcylinders; and an electro-hydraulic valve for receiving electricalcontrol signals from said controller to control the hydraulic pressureto each articulation cylinder.
 2. The steering system as set forth inclaim 1, wherein said at least one articulation cylinder has an extendedend position and a retracted end position and wherein said controllerdetects movement of said at least one articulation cylinder approachingone of said end positions and transmits electrical control signals tosaid electro-hydraulic valve to prevent an abrupt halt in the movementof said at least one articulation cylinder.
 3. The steering system asset forth in claim 1, wherein said controller detects an abrupt changein the position of said steering input control and transmits electricalcontrol signals to said electro-hydraulic valve to prevent an abruptchange in the control of hydraulic pressure to said at least onearticulation cylinder.
 4. The steering system as set forth in claim 1,wherein said controller monitors the position of said steering inputcontrol and transmits electrical control signals to saidelectro-hydraulic valve to match the position of said at least onearticulation cylinder with the position of said steering input control.5. A steering enhancing system for a vehicle, said system comprising:aoperator controlled steering input control for changing the direction ofsaid vehicle; a steering mechanism responsive to said steering inputcontrol for changing the direction of said vehicle, said steeringmechanism including at least one hydraulic cylinder operativelyconnected to said steering input control; sensors operatively connectedto said steering input control and said at least one hydraulic cylinder;and a computer control interconnected to said sensors and said hydrauliccylinder, said sensor sending signals to said computer control from saidsteering input control and said hydraulic cylinder; said computercontrol evaluating said signals and controlling said hydraulic cylinderbased upon said signals to enhance the steering of said vehicle.
 6. Thesteering enhancement system as set forth in claim 5, wherein at leastone hydraulic cylinder extends to fully extended and fully retractedpositions and wherein said computer control receives said signals fromsaid sensor as said hydraulic cylinder approaches either of said fullyextended or retracted positions, said computer control preventing anabrupt extension to either of said fully extended or fully retractedpositions.
 7. The steering enhancement system as set forth in claim 5,further including an electro-hydraulic unit interconnected between saidcomputer control and said at least one hydraulic cylinder, saidelectro-hydraulic unit controlling said at least one hydraulic cylinderin response to said computer control.
 8. The steering enhancement systemas set forth in claim 6, further including an electro-hydraulic unitinterconnected between said computer control and said at least onehydraulic cylinder, said electro-hydraulic unit controlling said atleast one hydraulic cylinder in response to said computer control. 9.The steering enhancement system as set forth in claim 5, wherein saidsensor detects abrupt changes at said steering input control and signalssaid computer control to override said steering mechanism and preventany abrupt change of said at least one hydraulic cylinder.
 10. Thesteering enhancement system as set forth in claim 9, further includingan electro-hydraulic unit interconnected between said computer controland said at least one hydraulic cylinder, said electro-hydraulic unitcontrolling said at least one hydraulic cylinder in response to saidcomputer control.
 11. The steering enhancement system as set forth inclaim 7, wherein said computer control monitors the position of saidsteering input control and transmits electrical control signals to saidelectro-hydraulic unit to match the position of said at least onehydraulic cylinder with the position of said steering input control. 12.An electro-hydraulic steering system for an articulated vehicle having afront frame and a rear frame, the system comprising:a controller; ahydraulic steering system including a pump; a steering input control; atleast one articulation cylinder; position sensors that transmit inputsignals to said controller; and an electro-hydraulic valve that receiveselectrical control signals from said controller and controls pressure tosaid at least one articulation cylinder.
 13. A steering enhancing systemfor a vehicle, said system comprising:a operator-controlled steeringinput control; a steering mechanism responsive to said steering inputcontrol, said steering mechanism including at least one hydrauliccylinder operatively connected to said steering input control; sensorsoperatively connected to said steering input control and said at leastone hydraulic cylinder; and a computer control interconnected to saidsensors and said hydraulic cylinder.
 14. A computer-controlled method ofelectro-hydraulic steering for an articulated vehicle having a frontframe and a rear frame, the method comprising the steps of:providinghydraulic pressure for a hydraulic steering system; transmittingmechanical steering inputs from a steering input control to saidsteering system; rotating said front frame with respect to said rearframe with at least one hydraulic articulation cylinder to steer saidvehicle; transmitting input signals from position sensors to acomputer-implemented controller for indicating the position of saidsteering input control and said at least one hydraulic articulationcylinder; processing said input signals with said computer-implementedcontroller; and transmitting electrical control signals from saidcomputer-implemented controller to an electro-hydraulic valve forcontrolling hydraulic pressure to said at least one hydraulicarticulation cylinder.
 15. The computer-controlled electro-hydraulicsteering method as set forth in claim 14, further comprising the stepsof detecting movement of said at least one hydraulic articulationcylinder approaching one of either a fully extended position or a fullyretracted position and transmitting electrical control signals to saidelectro-hydraulic valve to prevent an abrupt halt in the movement ofsaid at least one hydraulic articulation cylinder.
 16. Thecomputer-controlled electro-hydraulic steering method as set forth inclaim 14, further comprising the steps of detecting an abrupt change inthe position of said steering input control and transmitting electricalcontrol signals to said electro-hydraulic valve to prevent an abruptchange in the hydraulic pressure to said at least one hydraulicarticulation cylinder.
 17. The computer-controlled electro-hydraulicsteering method as set forth in claim 14, further comprising the stepsof monitoring the position of said steering input control andtransmitting electrical control signals to said electro-hydraulic valveto match the position of said at least one hydraulic articulationcylinder with the position of said steering input control.
 18. Acomputer-controlled method for enhancing the steering of a vehicle,comprising the steps of:inputting steering control for changing thedirection of said vehicle; responding to said input steering control tochange direction of said vehicle with a steering mechanism; sendingfirst signals from sensors responsive to said input steering control;sending second signals from sensors operatively connected to at leastone hydraulic cylinder; receiving said first and second signals at acomputer-implemented controller; evaluating said first and secondsignals by said computer-implemented controller; and controlling said atleast one hydraulic cylinder based upon said first and second signals toenhance the steering of said vehicle.
 19. The computer-controlledenhanced steering method as set forth in claim 18, further comprisingthe steps of receiving at a computer-implemented controller said secondsignals from said sensors as said at least one hydraulic cylinderapproaches either a fully extended or a fully retracted position andpreventing an abrupt extension or retraction of said at least onehydraulic cylinder to either of said fully extended or fully retractedposition, respectively.
 20. The computer-controlled enhanced steeringmethod as set forth in claim 18, further comprising the step ofcontrolling, in response to said computer-implemented controller, saidat least one hydraulic cylinder with an electro-hydraulic unitinterconnected between said computer-implemented controller and said atleast one hydraulic cylinder.
 21. The computer-controlled enhancedsteering method as set forth in claim 19, further comprising the step ofcontrolling, in response to said computer-implemented controller, saidat least one hydraulic cylinder with an electro-hydraulic unitinterconnected between said computer-implemented controller and said atleast one hydraulic cylinder.
 22. The computer-controlled enhancedsteering method as set forth in claim 18, further comprising the stepsof detecting abrupt changes of said input steering control and signalingsaid computer-implemented controller to override said steering mechanismto prevent any abrupt change of said at least one hydraulic cylinder.23. The computer-controlled enhanced steering method as set forth inclaim 22, further comprising the step of controlling, in response tosaid computer-implemented controller, said at least one hydrauliccylinder with an electro-hydraulic unit interconnected between saidcomputer-implemented controller and said at least one hydrauliccylinder.
 24. The computer-controlled enhanced steering method as setforth in claim 20, further comprising the steps of monitoring said inputsteering control and transmitting electrical control signals to saidelectro-hydraulic unit to match the position of said at least onehydraulic cylinder with said input steering control.